Abnormal surface liquid pH regulation by cultured cystic fibrosis bronchial epithelium

Cystic Fibrosis/Pulmonary Research and Treatment Center, School of Medicine, University of North Carolina, Chapel Hill, NC 27599-7248, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 01/2004; 100(26):16083-8. DOI: 10.1073/pnas.2634339100
Source: PubMed


Cystic fibrosis (CF) transmembrane conductance regulator (CFTR)-dependent airway epithelial bicarbonate transport is hypothesized to participate in airway surface liquid pH regulation and contribute to lung defense. We measured pH and ionic composition in apical surface liquid (ASL) on polarized normal (NL) and CF primary bronchial epithelial cell cultures under basal conditions, after cAMP stimulation, and after challenge with luminal acid loads. Under basal conditions, CF epithelia acidified ASL more rapidly than NL epithelia. Two ASL pH regulatory paths that contributed to basal pH were identified in the apical membrane of airway epithelia, and their activities were measured. We detected a ouabain-sensitive (nongastric) H+,K+-ATPase that acidified ASL, but its activity was not different in NL and CF cultures. We also detected the following evidence for a CFTR-dependent HCO3- secretory pathway that was defective in CF: (i). ASL [HCO3-] was higher in NL than CF ASL; (ii). activating CFTR with forskolin/3-isobutyl-1-methylxanthine alkalinized NL ASL but acidified CF ASL; and (iii). NL airway epithelia more rapidly and effectively alkalinized ASL in response to a luminal acid challenge than CF epithelia. We conclude that cultured human CF bronchial epithelial pHASL is abnormally regulated under basal conditions because of absent CFTR-dependent HCO3- secretion and that this defect can lead to an impaired capacity to respond to airway conditions associated with acidification of ASL.

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Available from: Larry G. Johnson, Feb 12, 2015
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    • "This protein pumps one cellular proton and one PCL K þ against their osmotic gradient, via the binding of ATP, and is localised to the apical membrane of lung epithelia (Coakley et al., 2003). The HKATPase pump provides basal proton secretion and K þ absorption across the apical membrane in airway epithelia (Fischer, 2012; Fischer et al., 2002; Poulsen and Machen, 1996; Smith and Welsh, 1993). "
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    ABSTRACT: The genetic disease cystic fibrosis (CF) is a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, and results in viscous mucus and impaired mucociliary clearance leading to chronic recurring pulmonary infections. Although extensive experimental research has been conducted over the last few decades, CF lung pathophysiology remains controversial. There are two competing explanations for the observed depletion of periciliary liquid (PCL) in CF lungs. The low volume hypothesis assumes fluid hyperabsorption through surface epithelia due to an over-active Epithelial Na(+) Channel (ENaC), and the low secretion hypothesis assumes inspissated mucins secreted from glands due to lack of serous fluid secreted from gland acini. We present a spatial mathematical model that reflects in vivo fluid recycling via submucosal gland (SMG) secretion, and absorption through surface epithelia. We then test the model in CF conditions by increasing ENaC open probability and decreasing SMG flux while simultaneously reducing CFTR open probability. Increasing ENaC activity only results in increased fluid absorption across surface epithelia, as seen in in vitro experiments. However, combining potential CF mechanisms results in markedly less fluid absorbed while providing the largest reduction in PCL volume, suggesting that a compromise in gland fluid secretion dominates over increased ENaC activity to decrease the amount of fluid transported transcellularly in CF lungs in vivo. Model results also indicate that a spatial model is necessary for an accurate calculation of total fluid transport, as the effects of spatial gradients can be severe, particularly in close proximity to the SMGs. Copyright © 2015. Published by Elsevier Ltd.
    Journal of Theoretical Biology 07/2015; 382. DOI:10.1016/j.jtbi.2015.06.050 · 2.12 Impact Factor
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    • "First, loss of CFTR impairs HCO 3 – secretion across airway epithelia cultured from humans [4] [5] and pigs with a disrupted CFTR gene [6]; CF pigs spontaneously develop lung disease that mimics human CF [7]. Second, loss of CFTR reduces the pH of airway surface liquid (ASL) in cultured human airway epithelia [5], of secretions from human submucosal glands studied ex vivo [8], and of ASL studied in vivo, ex vivo, and in epithelial cultures from CF pigs [9]. Third, a reduced pH decreases the activity of antimicrobials in ASL in vivo and in vitro, thereby "
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    ABSTRACT: Disrupted HCO3(-) transport and reduced airway surface liquid (ASL) pH in cystic fibrosis (CF) may initiate airway disease. We hypothesized that ASL pH is reduced in neonates with CF. In neonates with and without CF, we measured pH of nasal ASL. We also measured nasal pH in older children and adults. In neonates with CF, nasal ASL (pH5.2±0.3) was more acidic than in non-CF neonates (pH6.4±0.2). In contrast, nasal pH of CF children and adults was similar to values measured in people without CF. At an age when infection, inflammation and airway wall remodeling are minimal, neonates with CF had an acidic nasal ASL compared to babies without CF. The CF:non-CF pH difference disappeared in older individuals, perhaps because secondary manifestations of disease increase ASL pH. These results aid understanding of CF pathogenesis and suggest opportunities for therapeutic intervention and monitoring of disease.
    Journal of cystic fibrosis: official journal of the European Cystic Fibrosis Society 01/2014; 13(4). DOI:10.1016/j.jcf.2013.12.006 · 3.48 Impact Factor
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    • "The airway epithelium is covered by a thin layer of surface liquid (ASL), which is vital for maintaining a healthy respiratory tract. It is now well established in cystic fibrosis (CF) that a lack of functional cystic fibrosis transmembrane conductance regulator (CFTR) impairs airway bicarbonate and fluid secretion producing an acidic, viscous ASL [1], [2], [3] that is readily colonised by bacteria such as Pseudomonas aeruginosa [4]. Much has been made of the defective anti-microbial properties of the CF ASL and of changes in host-pathogen responses across the CF airway epithelium. "
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    ABSTRACT: People with cystic fibrosis (CF) who develop related diabetes (CFRD) have accelerated pulmonary decline, increased infection with antibiotic-resistant Pseudomonas aeruginosa and increased pulmonary exacerbations. We have previously shown that glucose concentrations are elevated in airway surface liquid (ASL) of people with CF, particularly in those with CFRD. We therefore explored the hypotheses that glucose homeostasis is altered in CF airway epithelia and that elevation of glucose flux into ASL drives increased bacterial growth, with an effect over and above other cystic fibrosis transmembrane conductance regulator (CFTR)-related ASL abnormalities. The aim of this study was to compare the mechanisms governing airway glucose homeostasis in CF and non-CF primary human bronchial epithelial (HBE) monolayers, under normal conditions and in the presence of Ps. aeruginosa filtrate. HBE-bacterial co-cultures were performed in the presence of 5 mM or 15 mM basolateral glucose to investigate how changes in blood glucose, such as those seen in CFRD, affects luminal Ps. aeruginosa growth. Calu-3 cell monolayers were used to evaluate the potential importance of glucose on Ps. aeruginosa growth, in comparison to other hallmarks of the CF ASL, namely mucus hyperviscosity and impaired CFTR-dependent fluid secretions. We show that elevation of basolateral glucose promotes the apical growth of Ps. aeruginosa on CF airway epithelial monolayers more than non-CF monolayers. Ps. aeruginosa secretions elicited more glucose flux across CF airway epithelial monolayers compared to non-CF monolayers which we propose increases glucose availability in ASL for bacterial growth. In addition, elevating basolateral glucose increased Ps. aeruginosa growth over and above any CFTR-dependent effects and the presence or absence of mucus in Calu-3 airway epithelia-bacteria co-cultures. Together these studies highlight the importance of glucose as an additional factor in promoting Ps. aeruginosa growth and respiratory infection in CF disease.
    PLoS ONE 10/2013; 8(10):e76283. DOI:10.1371/journal.pone.0076283 · 3.23 Impact Factor
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